I2O: handle sysfs_create_link() failures

Compile warning:
ignoring return value of `sysfs_create_link', declared with attribute warn_unused_result.

If sysfs_create_link failed, take care of the return value and do some
error handle after the failure.

Since sysfs_remove_link() will check whether a link exists, when removing the
link in error path, we don't need to care whether a link was created.

Signed-off-by: Wang Chen <wangchen@cn.fujitsu.com>
Cc: Markus Lidel <Markus.Lidel@shadowconnect.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>